How do snakes hear ?

Snakes do not have ears or ear openings outside the body like us. They have inner ears inside the head.
When an animal or person walks, vibrations are caused. These pass through the earth to the body of the snake. The vibrations pass through the skin and muscles of the snake to a bone connected to its inner ear. This bone passes the vibrations to the ear, which 'hears' them.
Likewise snakes also hear sounds or vibrations that travel through the air. Their skin, muscles and bone carry the vibrations to the inner ear. Of course the vibrations that travel in the air are not as clear as that travel on the ground.